In emacs 23.1, all tag names have font “function-name”, and attributes have “variable-name.”

In emacs 23.2, the fontification is more complex.
Most tag names have the font property of “nxml-element-local-name”.
Attributes have “nxml-attribute-local-name”.
Attribute values has “nxml-attribute-value”.
Double quotes has “nxml-attribute-value-delimiter”.
The slash in ending tags is “nxml-tag-slash”.
Angle brackets < and > are “nxml-tag-delimiter”.

Normally you wouldn't notice this, but you would if you regularly use
htmlize
to turn a buffer into HTML code.
Then, you'll see that that each font name gets turned into a span tag,
and the 23.2's version is much more verbose.

The original is 492 chars, now it is 5627 chars, about 10 times larger.

Every left angle bracket < becomes:

<spanclass="nxml-tag-delimiter">&lt;</span>

Right angle bracket > becomes:

<spanclass="nxml-tag-delimiter">&gt;</span>

For every double quote, now it becomes:

<spanclass="nxml-attribute-value-delimiter">"</span>

and slash / in closing tags become:

<spanclass="nxml-tag-slash">/</span>

In emacs 23.1, the angle brackets are simply &lt; and
&gt;, slash and double quote are left as is.

What Does It Mean?

So, this means, if you have a lot web pages showing XML code in color, such as a XML tutorial, the page file size will now be several times larger.

Though, overall i'm not sure this is a problem. The fontification
in emacs simply improved by being more exact and elaborate. When you
turn buffer fontification into HTML/CSS code, naturally you got this
huge number of span tags, and that's just the design of HTML. But
overall, the web today has video streaming all over, so few kilo bytes
is trivial, and doesn't take more time for browser to parse it than say
loading a single image file.

If you look at any of the top site's HTML source code, most of them are not human readable since about ~2003.